Semiconductor integrated circuits have been developed to have high performance and high integration in response to miniaturization of devices. In recent years, miniaturization is being advanced in the device design rules, but optical lithography that is a main technique of miniaturization is approaching the practical limit.
In order to obtain highly miniaturized patterns, it is necessary to reduce a pitch of a pattern, which is the sum of the width of the pattern and the interval between adjacent patterns. It is relatively easy to narrow the width of the pattern by exposure. However, it is relatively difficult to form fine patterns at a short pitch. In the optical lithography, it is a challenge to shorten the pitch when the fine patterns are formed.
As a technique for forming fine patterns at a short pitch, a technique called double patterning has been developed (see, e.g., Patent Document 1). Double patterning is a technique for forming two patterns in one pitch to double the pattern as the name implies.
Patent Document 1: Japanese Patent Application Publication No. 2008-193098
In the double patterning technology, a step of etching a silicon oxide film formed on a silicon nitride film is required. In this case, it is requested to suppress a recess from being formed in the silicon nitride film by increasing the selectivity of the silicon oxide film with respect to the silicon nitride film.
However, the binding energy of Si—O is 111 eV, and is higher than the binding energy of Si—N which is 105 eV. Thus, in a state in which both the silicon oxide film and the silicon nitride film are present, it is physically difficult to increase the selectivity of the silicon oxide film with respect to the silicon nitride film. This is because the silicon nitride film is also etched when the silicon oxide film is etched by increasing the ion energy of the plasma. Therefore, not only a physical approach such as increasing the ion energy of the plasma, but also a chemical approach using a difference in reactivity between the surfaces of the silicon oxide film and the silicon nitride film is necessary.